1. Field of the Invention
The present invention relates generally to a method for preventing the development of biofouling on the surface of structures that come into contact with aquatic environments. Specifically, the invention relates to the use of a laminated heater element impermeable to water, disposed on the surface of such structures to prevent biofouling on the surface.
2. Description of the Prior Art
Biofouling is defined as the settlement and attachment of aquatic plants and animals onto hard substrates introduced into the aquatic environment by human activity. Biofouling can occur within both marine and freshwater systems. Biofouling is initiated by the establishment of a film of bacteria on the newly submerged surface. The bacterial film promotes the colonization of larger multicellular species on the surface through the enhancement of larval settlement, specifically by inducing a metamorphosis in the fouling organism from a mobile larval stage to a sessile juvenile stage.
Biofouling on fixed or suspended structures in the water, such as docks, buoys, power plant inlet-outlet water pipes, or oil drilling platforms can cause a variety of problems. The weight of the fouling biomass places undue stress on the structure. In addition, the biomass promotes metal corrosion or degradation of wood products, and reduces the visibility of submerged structures during inspections. Biofouling on ships occurs when ships are at dockside rather than when they are at sea, but the fouling organisms increases drag on the hull while the ship is moving. Barnacle fouling alone can raise fuel consumption of an oceangoing ship by 40% (Christie A. A. and R. Dalley. 1987. Barnacle fouling and its prevention. In: A. J. Southward (ed.) Barnacle Biology. A. A. Balkema. Rotterdam, NL. pp. 419-433).
Fouling organisms are comprised of between 4,000 and 5,000 different species within the marine environment alone (Crisp, D. J. 1972a. The role of the biologist in anti-fouling research. In: R. F. Acker, B.F. Brown, J. R. DePalma, and W. P. Iverson (eds.) Proceedings of the Third International Congress on Marine Corrosion and Fouling). It is virtually impossible to fully understand the biological characteristics of every fouling organism and to individually derive a means for controlling every single fouling species in the world. Therefore, control of fouling is approached by grouping fouling organisms into biologically relevant groups and selecting key species as representatives of each specific group. The key species for each general group are usually those species which are either the most common fouling organisms and/or a typical species that is well researched and understood, such as the marine algae, Enteromorpha and Ectocarpus species, which are considered the primary fouling genera; barnacles within the genus Crustacea; blue mussels of Mytilus edulis, and the zebra mussel within the Dreisseria polymorpha.
The dispersal of sessile aquatic organisms generally occurs during the early life stages of the organism. Many sessile organisms are mobile in early life. As the mobile larvae grow and mature, however, the organism seeks an appropriate surface for attachment. Larval settlement involves the organism undergoing a metamorphosis to its adult life form. This change involves an attachment to a hard surface either permanently, as in the case of barnacles cementing to a substrate, or temporarily, as in the case of mussels attaching to a substrate with byssal threads. The compositions used by organisms for both permanent or temporary attachment are predominantly proteins that are extensively cross-linked and therefore relatively impervious to external influences (Crisp, D. J. 1972b. Mechanisms of adhesion of fouling organisms. In: R. F. Acker, B. F. Brown, J. R. DePalma, and W. P. Iverson (eds.) Proceedings of the Third International Congress on Marine Corrosion and Fouling. National Bureau of Standards, Gaithersburg, Md. pp. 691-709). As such, the ideal means to control fouling is to stop it at its first settlement stage rather than later when the cemented structures are very difficult to remove.
Researchers have long attempted to develop means to effectively control biofouling. Fouling problems can be approached using a few basic considerations. These general approaches encompass:
1) killing the larvae as they contact the settlement surface; PA1 2) discouraging the larvae from choosing the surface for settlement; or PA1 3) interfering with the chemical processes involved with adhesion.
A variety of methods for controlling biofouling utilizing these approaches have been attempted. These methods include the use of mechanical, chemical and electrical eradication means to discourage settlement before it occurs or eradicate settlement after it has occurred. Acoustic, ultraviolet and thermal eradication and/or preventive methods have also been attempted. However, to date, a truly effective means for preventing such biofouling has not been developed.